part 1 ques

Enteric gram-negative bacteria are more resistant to penicillin G than gram-positive bacteria. Which of
the following is most closely associated with this difference?
(A) Cytoplasmic membrane
(B) Lipoprotein
(C) Outer membrane
(D) Peptidoglycan
(E) Teichoic acid

Penicillin works by inhibiting crosslinking in peptidoglycans. Gram positive bacteria have thick peptidoglycan walls while gram negatives have thin peptidoglycan walls. If it helps, recall that penicillins are most effective when bacteria are in their log phase of growth, when the peptidoglycan wall is forming most rapidly.

I believe teichoic acid is indeed a component of the gram positive bugs, but it has no direct connection to penicillin.

Mechanism of action
Main article: beta-lactam antibiotic
&#946;-lactam antibiotics work by inhibiting the formation of peptidoglycan cross-links in the bacterial cell wall. The &#946;-lactam moiety (functional group) of penicillin binds to the enzyme (DD-transpeptidase) that links the peptidoglycan molecules in bacteria, which weakens the cell wall of the bacterium (in other words, the antibiotic causes cytolysis or death due to osmotic pressure). In addition, the build-up of peptidoglycan precursors triggers the activation of bacterial cell wall hydrolases and autolysins, which further digest the bacteria's existing peptidoglycan.

Gram-positive bacteria are called protoplasts when they lose their cell wall. Gram-negative bacteria do not lose their cell wall completely and are called spheroplasts after treatment with penicillin.

Penicillin shows a synergistic effect with aminoglycosides, since the inhibition of peptidoglycan synthesis allows aminoglycosides to penetrate the bacterial cell wall more easily, allowing its disruption of bacterial protein synthesis within the cell. This results in a lowered MBC for susceptible organisms.

Its the outer cell membrane that slows or in some cases of penicillin binding proteins actually transports the penicillin out of the outer cytoplasmic space thus decreasing the activity

Click to expand...

I agree with you on this one. It cannot be peptidoglycan as its present in both +ve and -ve organisms and thats not the difference (not teichoic acids as its present only in +ve and peniclillin does not act on it).
I would go with outer membrane.

Mechanism of action
Main article: beta-lactam antibiotic
&#946;-lactam antibiotics work by inhibiting the formation of peptidoglycan cross-links in the bacterial cell wall. The &#946;-lactam moiety (functional group) of penicillin binds to the enzyme (DD-transpeptidase) that links the peptidoglycan molecules in bacteria, which weakens the cell wall of the bacterium (in other words, the antibiotic causes cytolysis or death due to osmotic pressure). In addition, the build-up of peptidoglycan precursors triggers the activation of bacterial cell wall hydrolases and autolysins, which further digest the bacteria's existing peptidoglycan.

Gram-positive bacteria are called protoplasts when they lose their cell wall. Gram-negative bacteria do not lose their cell wall completely and are called spheroplasts after treatment with penicillin.

Penicillin shows a synergistic effect with aminoglycosides, since the inhibition of peptidoglycan synthesis allows aminoglycosides to penetrate the bacterial cell wall more easily, allowing its disruption of bacterial protein synthesis within the cell. This results in a lowered MBC for susceptible organisms.

Click to expand...

Yes it does indeed work on the peptidoglycan cross-links but that is not the reason why they are more resistant. Gram - have an outer membrane(LPS, which consists of lipid A, core polysaccharide, and O antigen) which makes it more resistant to the effects of penecillin. Hence when you cited your article from wiki gram negatives usually don't lose their cell membrane completely and form speroplast. Also the peptidoglycan layer is not as accessible since it has an outer membrane surrounding it(this is what i use to remember it, but it plays less of a role in the resistance.

I believe that is the answer they are looking for. However I would probably disagree with all of them. Members of the family Enterobacteriaceae commonly express plasmid-encoded &#946;-lactamases (e.g., TEM-1, TEM-2, and SHV-1) which confer resistance to penicillins but not to expanded-spectrum cephalosporins. Not sure when that question was originally asked but drug resistance has had quite a bit of research done on it as of late.

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